1. Field of Invention
The present invention relates to inductances with shared values formed on a semiconductor substrate, and especially to such inductances intended for operating in a range of frequencies greater than several hundreds of MHz, which will be here called the RF range.
2. Description of the Related Art
FIG. 1 schematically shows a perspective view of an inductance L integrated on a semiconductor substrate 1, intended for operating in the RF range. Inductance L includes a substantially planar conductive track 2 deposited on a first insulating layer 5 of the semiconductor substrate. Conductive track 2 forms a winding comprised of a succession of rectilinear segments arranged between a first end 3, on the external side of the winding, and a second end 4, on the internal side of the winding. The rectilinear segments forming the winding are substantially parallel two by two and separated by a constant distance. A first terminal A of inductance L is formed by end 3 of track 2. A second terminal B of inductance L is connected to end 4 of track 2 via a conductive segment 6 passing under the segments of track 2.
FIG. 2 schematically shows a circuit 8 for receiving RF signals using integrated inductances. Circuit 8 includes a first processing chain T1 enabling reception of signals modulated on a carrier of frequency f1, for example, on the order of 900 MHz, and a second processing chain T2 enabling reception of signals modulated on a carrier of frequency f2, for example on the order of 1800 MHz. Such a circuit is useable in a device like a cell phone provided for operating either only with frequency f1, or only with frequency f2, or indifferently with one of frequencies f1 or f2.
Circuit 8 includes an input 10 connected to an antenna 12. The first processing chain T1 includes a low-noise amplifier 14, a mixer 16, and a first local oscillator (not shown). Amplifier 14, provided for amplifying signals modulated on a carrier of frequency f1, is connected to input 10 and provides a differential signal to mixer 16. Mixer 16 further receives a sinusoidal signal of frequency f11 provided by the first local oscillator. It provides a signal of intermediary frequency IF=f1−f11 to an output 18. The second processing chain T2 includes a low-noise amplifier 20, a mixer 22, and a second local oscillator (not shown). Amplifier 20, provided to amplify signals modulated on a carrier of frequency f2, is connected to input 10 and provides a differential signal to mixer 22. Circuit 22 also receives a sinusoidal signal of frequency f12 generated by the second local oscillator and provides a signal of intermediary frequency IF=f2−f12 to output 18, the intermediary frequencies provided by mixers 16 and 22 being the same. A control means (not shown) activates one of the processing chains according to the desired frequency.
Mixer 16 includes a so-called “Gilbert cell” (not shown), having terminals G1 and G2 respectively connected to the first terminals A1, A2 of two inductances L1 and L2. The second terminals B1 and B2 of inductances L1 and L2 are connected to the circuit ground. Inductances L1 and L2 have equal values. When the Gilbert cell operates, the alternating currents flowing through inductances L1 and L2 have the same frequency, the same absolute value, and opposite directions. The value of inductances L1 and L2 is inversely proportional to the operating frequency.
Similarly, mixer 22 includes a Gilbert cell (not shown) having two terminals G3 and G4 respectively connected to the first terminals A3, A4 of two inductances L3 and L4. The second terminals B3, B4 of inductances L3 and L4 are connected to the circuit ground. Inductances L3 and L4 have equal values. Frequency f2 being greater than frequency f1, inductances L3 and L4 have a value smaller than that of inductances L1, L2.
In an implementation in integrated form of circuit 8, the four inductances L1, L2, and L3, L4 occupy a significant surface area, which increases the cost of the integrated circuit.